1. Field of the Invention
The present invention relates to a rigid graduated element in a position measuring system, wherein the graduated element is fixed in place on the holder by resilient elements engaging the circumferential face of the graduated element in that the graduated element is clasped in several directions X, Y by the resilient elements and wherein each resilient element exerting a force on the graduated element in one direction is assigned at least one further resilient element which exerts a force on the graduated element in the other direction and maintains the graduated element in an equilibrium.
2. Discussion of Related Art
A widely employed type of fastening a graduated element on a holder is that of gluing. However, it has been shown that gluing does not assure an acceptable stability of the position of the graduated element on the holder. Drifting of the graduated element has been noticed because of the shrinkage of the adhesive over time, the large coefficient of temperature of the adhesive, and the change in its volume in case of moisture.
Therefore gluing is not used in highly precise position measuring systems, and the graduated element is fastened to the holder by clamping. Such a holder of the graduated element is known from EP 0 264 801 A1. For a long term stable and reproducible fastening of the graduated element, the latter is urged against a face of the holder by springs acting on a narrow side. Spheres between this face of the holder and the graduated element make the seating of the graduated element possible and allow rolling movements with respect to the holder.
However, it has been found that this arrangement still results in measurement errors in case of temperature changes. The reason for this is frictional forces arising between the holder and the graduated element during temperature changes.